The 8% increased in cargo size translates into an 8% increase in trade/refinery income.  Whether or not this is cost-effective depends on how many trade ports you have and what your current logistics situation is.

The break-even point is usually about 19 trade ports.  Once you've built your 19th trade port, this investment makes sense.  Of course, you should always prioritize expanding your existing trade route, but that's not always an option.  Sometimes the thorny issue of logistics also rears its head; if you don't have logistics space for new trade ports, but you still have a considerable network (say 10 or more) this upgrade is still viable because it won't use those logistics spaces.

is it worth it to not put a trade port at a certain planet just to avoid breaking the trade route? 

what if i put multiple trade ports at that plated that brake the line ?? i normaly just span trade ports everywhere after i get all 16 labs

You can accidentally shorten your chain by placing a new port.  Suppose we have this planet layout:

A   == B ==  C
||                  ||
D   == E ==  F

If you put trade ports on every planet, your longest route is halfway around the circle (3 jumps).  However, if we remove a trade port from B, our longest route is now A-D-E-F-C, a superior 4 jumps.  So yes, you can accidentally reduce your trade length by placing ports on new planets.

Fair enough I thought the game handled it differently.