These two matches can make big changes on the ranking table because despite of worse performances than expected, Roma have only 3 points less than Juventus, and Lazio have the same points as Juventus but only 1 point less than Inter Milan.
If Lazio beats Inter Milan, they will get a second position from the opponent and if Roma beat Juventus, they will have same total points as the opponent. Lazio and Roma are considered as weaker teams than their opponents but if they can win, Serie A will be more exciting with big changes in positions of top clubs. If these matches end without winners, other clubs can flip top positions of Inter Milan, Juventus and Lazio so I bet that they will not want a draw this weekend.
Juventus and Lazio are very close, so it could be a cautious match, they won't want to lose their positions, maybe Juventus will try to win this match, but I can't understand yet how ambitious Motta is to fight for the Scudetto.
And for Roma, everything is more difficult, because Inter is clearly stronger than them now and the most important task for them now is to stay as close to Napoli as possible. For Roma, this match will also be of great importance, you correctly noted, there are only three points between Roma and Juventus, so they will certainly try to win, but it seems to me that Inter will not allow this to happen now.