Do the cams need stronger springs to accommodate higher rpm or are the to keep the valve train following the new more aggressive profile? If it's only for rpm and you're content to keep the stock rev limit, you could keep the original soft springs? Just thinking aloud, here. I got no cams.
Technically, it would be for both.
For a higher lift to occur in a similar duration, the acceleration is greater, and needs more spring pressure to keep the valve under control. Even with a longer duration, the profile is often ground with steeper flanks to get as much time at higher lifts as possible. Add to that, the fact that most performance cams aim to get more hp, and hp is a product of tq and rpm, the generally aim to increase the peaks of both tq and hp rpms.
So yes, in many/most cases with performance cams, new stronger springs are a necessary part of the program. Pretty much any cam maker will tell you that.
The amount of spring pressure needed depends on the cam profile, the moving masses, and the rpms targeted. Beehive type springs can control the valve at lower pressures than conventional springs, due to their inherent design benefits, but there are limits.
If accelerations and mass and rpms are not changed, but the cam timing is different, then the same springs should be able to be used. For example, if you re-phased the factory cams in either direction, you could keep the factory springs because the cam lobes are still the same as before even though the timing is changed.