5 research points would be enough to enable a single researched first tier unit type for mass production. If I wish to rely on grenadiers, shamans and armors I'd need to research shamans (5), armors (10), field grenadiers (5), field shamans (5) and field armors (10), which would be an added cost of 20 research points. However, simply spending 5 on any one first tier unit is enough that you can mass produce units in RTS at your regular pace. You're going to do at least that much before your first battle, I'm sure; but which unit? You wouldn't want to invest in many. Maybe just armor? Maybe just warlock?
The adjustment of +5 research points is alotted for you to enable one tier 1 unit for RTS production. However, you may choose to invest more (or forgo it entirely, which seems like a bad idea).