Main purpose
Keeping heat charges accumulation and viral status on enemies.
Guaranting a Crit. Tier upgrade.

How does it work?
Heat status accumulation is good for a mid - long term fight ( 2 - 5 mins ) and decreases enemy armor up to 50%.
Viral status is good for enemies where you need to deal more damage to Health Points, up to 325%.

Its status / second (SPS) is done by:
SPS = Fire rate x Multishot x (%status / 100) = 17,4 x 1,6 x 1,25 = 34,8

As long as Heat charges have no limit and Viral caps around 10, the SPS excess goes to Heat accumulation.

Finally...
" When a weapon achieves a status chance higher than 100%, each hit may apply additional status effects. The type of each proc is independently drawn, so it is possible to apply the same status several times in one hit. "

References:
https://warframe.fandom.com/wiki/Damage/Heat_Damage
https://warframe.fandom.com/wiki/Damage/Viral_Damage
https://warframe.fandom.com/wiki/Set_Mods#Vigilante_Mod_Set
https://warframe.fandom.com/wiki/Critical_Hit#Crit_Tiers
https://warframe.fandom.com/wiki/Fire_Rate
https://warframe.fandom.com/wiki/Status_Effect