Basically, this affects the determination of the OU list. If all Rotom forms are considered one Pokemon, then Rotom is OU. If not, then each form is not OU.
In my opinion, there are two different forms of Rotom that play differently: the original Rotom having 50/50/77/95/77/91 base stats, and the appliances Rotoms having 50/65/107/105/107/86 base stats. Since these two have different stats, then they should be treated separately, just like we treat the usages of Deoxys-A, Deoxys-D, Deoxys-S and regular Deoxys separately in ubers. However, all the 5 appliances Rotom should be treated as one Pokemon. That's my opinion.
So, basically, our options are:
1) Treat all Rotom forms (including the original Rotom) as one Pokemon.
2) Treat the original Rotom as one Pokemon and the other Rotom forms as another Pokemon.
3) Treat each of the six Rotom forms (the original and 5 appliances) as different Pokemon.
As I said before, I would choose option 2).
In my opinion, there are two different forms of Rotom that play differently: the original Rotom having 50/50/77/95/77/91 base stats, and the appliances Rotoms having 50/65/107/105/107/86 base stats. Since these two have different stats, then they should be treated separately, just like we treat the usages of Deoxys-A, Deoxys-D, Deoxys-S and regular Deoxys separately in ubers. However, all the 5 appliances Rotom should be treated as one Pokemon. That's my opinion.
So, basically, our options are:
1) Treat all Rotom forms (including the original Rotom) as one Pokemon.
2) Treat the original Rotom as one Pokemon and the other Rotom forms as another Pokemon.
3) Treat each of the six Rotom forms (the original and 5 appliances) as different Pokemon.
As I said before, I would choose option 2).