The creators have said that the season pass will bring 8 new operators (2 which are being revealed in February Dlc) to those who hold the season pass with all others having to use renoun to purchase them.
Alongside making the 8 operators available the season pass brings various weapon skins with each Dlc release (the safari skin pack is available as soon as the season pass is purchased).New weapons with each Dlc operator are available straight away.Season pass holder get a 600 credited to their Rainbow credits to use how they see fit and also a 5% permanent boost to their renoun that is gain when playing.
The creators have also said that the season pass will bring more to those that hold it which hasn't been leaked in regards to anything on or posted on the net.
Suppose it comes down to personal preference but I know il be playing this game for quite a long time so it made sense for myself to purchase it.