Many fans scratched their heads when Chelsea made a move for Welbeck and Henderson in the summer transfer window.
Both players are not automatic starters and will not make an immediate impact for Chelsea on the pitch.
However, Welbeck and Henderson can drive standards in training, organise players and mentor the younger players behind the scenes.
Speaking ahead of Chelsea’s clash with Brighton on Sunday, Alonso praised the pair who were signed to set an example in a Blues side who are known for their young squad.
"I am aware (of his record in the fixture) and I am happy he is with us!
"He (Welbeck) has many qualities. As a player, you see how intelligent he is, and he links well. Out of the box, he is able to combine, and in the box he is very intelligent to be in the right place. We saw that (against Luton).
"On a daily basis, he is a great influence for the rest of the players. He trains really hard and is raising all the standards in training. This is something we think is important.
"They help but it’s not just them. Reece (James), Maxence (Lacroix), Morgan (Rogers) as well. Even if they are younger, they have a good impact.
"That was a very important decision in the squad planning - that we were bringing players who add not just on the field, but are ready to compete and who don’t need much time to make an impact. We are happy with that."
Welbeck and Henderson will hope to make an impact on Sunday against the Seagulls, as players look to the pair for inspiration, especially as Welbeck faces his former side.