Will the Battery of my MacBook Pro 15" 2016 deteriorate if it is plugged in charging all day?

You may get a lot of opinions on this, and also potentially risk having your question closed because it is primarily opinion-based.

However, I will try and answer this solely by keeping it to the facts.

Firstly, you should read what Apple has to say about their batteries.

In summary:

• Charge your MacBook Pro battery as it suits you. You do not need to let the battery discharge 100% (or any percent) before recharging.
• Apple have designed their lithium-ion batteries to reach 80% of their capacity quickly and then switch to a slower trickle charge to complete the other 20%.
• Ambient temperature is a big factor in determining battery health/life. Your MacBook Pro is designed to work at its best when ambient temperatures are between 16° to 22° C (62° to 72° F).
• Avoid exposing your MacBook Pro to ambient temperatures higher than 35° C (95° F)
• If you ever need to store your MacBook Pro long-term without being used, then ensure it is switched off and the battery is only half charged.

Finally, the latest research (2016) has found that the biggest cause for ruined batteries is time. In other words, you can purchase a brand new MacBook Pro battery and leave it in a cupboard for five years* and then find it's capacity is greatly diminished when you finally start using it.

*Just an example - the research did not specify a 5yr period.

[EDIT - Time a key factor in battery degradation]

I was hoping to edit my answer to cite a source (and provide a link) re my paragraph above about the latest research showing that time on its own is one of the key causes of the degradation of Lithium ion batteries. Unfortunately, while I thought I had the research saved in my Reading List and bookmarks, I wasn't able to find it - so will keep searching and will add it in due course.

However, just to elaborate a bit on this (and other) research, it is still clear there are a number of factors that affect Lithium batteries: the State of Charge (SoC) - both during storage as well as at commencement of charge - charge cycles generally, the recently discovered (in 2014) formation of crystals as lithium ions pass through cathodes and anodes, and so on.

The new finding from the research I was wanting to cite was primarily that a Lithium battery does actually start to degrade after manufacture as a result of time, regardless of how it is (or isn't) used (although the effect of this is pronounced by the number of charge cycles etc). I did find this quote from an ABC Science News article that may be based on the research I'm looking for:

Lithium batteries don't age gracefully

From the moment they're made, lithium ion batteries start losing their ability to store charge and generate a voltage over time. It's called ageing, and it happens whether they're being used or not, so check the date of manufacture when you buy a lithium ion battery.

The ageing is caused by chemical changes at the electrodes. The positive electrode isn't a solid lump — it's made of microscopic particles of a lithium-based material. Over time those particles coalesce together forming bigger lumps, so there's less surface area for the lithium-releasing reaction when the battery is being used (discharging).

And recharging doesn't send 100 per cent of the lithium ions back to the negative electrode — some ions always get permanently stuck to the positive electrode. So over time there are fewer positive lithium ions 'in play' in the battery.

Source: http://www.abc.net.au/news/2016-02-15/rechargeable-batteries-how-they-work-why-they-blow-up/7081286

This finding is particularly relevant because many people still buy a second or spare battery and mostly keep them in cupboards until they eventually need them, but the better process would be to swap the batteries regularly to lengthen the overall lifespan/health of both batteries.

Regardless, I am sure we will see lots of research (and some of it contradictory) and the advice offered by Apple (and others) will change over time. I still remember Apple offering an iCal reminder (via a .ics file download) that users could download to remind them to charge and discharge their MacBook batteries! Now they don't even tell people to bother, let alone offer a downloadable reminder!

To my knowledge it is more or less a consensus that Li-Ion batteries require regular discharge to keep the electrons moving. This article is one of the most comprehensive I know on the issue. It states that one should avoid low and high temperatures, regular deep discharges, and permanent full charges. The author recommends to use the battery from time to time with shallow discharge cycles.