Is it worth it to remove Item Modifications?

In SWTOR you can put various modifications into various items that you wear/use -- and you can remove these and put new ones in, at a charge.

Is it worth it to remove them and sell them, if you're not planning on reusing the items (obviously if you intend t reuse them, it makes sense)? Or will the cost to remove them always be greater than the amount earned by selling them?

You cannot remove mods and sell them to other players.

Once you remove the mod the item and mod becomes bound to you and then the only person that you can sell the weapon/armor/mod to is a vendor.

If you are talking about removing the mod just to sell, the cost of removing it is greater than the cost of the mod itself when sold to a vendor.

In one particular case — yes. The Offhand items from the Level 8 Equipment Vendor (on Fleet) have Armorings/Hilts/Barrels that cost 35 credits to rip out, but sell for 100 credits. The items themselves sell for 4395 credits after doing the above, so it's a really good way to convert Common Data Crystals (6 each) into credits.

Of course, if you have a Cartel crystal unlocked you can redeem a copy for free and insert it into the item, and then just sell the whole item for 4495. So as with the general case, you're still losing potential money by taking out the mod.