I can give something that this could be used.
1) Artilery weapons - super powerfull weapons that need to be stationary or very slow to fire
2) Unstable Shields - shield would turn off or weaken if speed it too high (Shields for capital ships that should move slower but are more powerful)
3) Normal travelling betwen systems - if ship goes fast enought then some kind of block with ftl component is charging so you can jump with something cheaper with less fuel usage
4 )bombing(?) wepons - a weapon that have to go fast to even fire
5) Ramming weapons that deal damage after certain speed is reached
6) just cool indicator that shows what the speed is ( sadly probably only in few stages like black, green yellow orange, red ... or numbers 1,2...)
