Are planche leans important when learning the Planche?

Are they valuable in developing the strength, or should I stick with Tuck planches

Very important. Unless you have been doing them for a while and they are no sweat and you have a solid 30+ sec tuck planche, planche leans should be in your training.

As Christian said, very important. Read the link underneath I must have reposted this link at least 10 times. It's a very good read.

https://www.gymnasticbodies.com/forum/topic/5959-scapula-position-for-basic-and-static-exercises/

Planche leans can always be made harder, by leaning forward more. Once you can hold one for 20-30 seconds with your hands at hip level, you can elevate your feet and begin building up strength there.