The more delta-v you require (so plus or minus that 500km/h) and the more payload you have, the more rocket you need. If you have fixed rocket size and/or a fixed budget, launching at high latitude translates into either less delta-v left over to go places or less payload.
There are partial or full exceptions if you’re launching into certain orbits. For a mapping satellite that goes straight north/south as the Earth rotates below I would guess you might even prefer a higher-latitude launch.
Necessary, no. Better, yes.
The more delta-v you require (so plus or minus that 500km/h) and the more payload you have, the more rocket you need. If you have fixed rocket size and/or a fixed budget, launching at high latitude translates into either less delta-v left over to go places or less payload.
There are partial or full exceptions if you’re launching into certain orbits. For a mapping satellite that goes straight north/south as the Earth rotates below I would guess you might even prefer a higher-latitude launch.