They could do a lot of damage.
Personally I think this whole 'China is helping the Taliban' thing stems from the fact that some Chinese authorities are trying to find a way to contain that threat. The threat is far more than just in the West too. There are Muslims all over China.
The Muslims inside of China (not just the in the West) could well represent another 'hui' inside of China. In CCP eyes, "hui" = popular uprising.
If they try to crush all the Muslims then they have a problem for sure. Therefore the only other option is to make friends. That is most likely exactly why the Taliban was invited to Beijing a few years back, etc.
They might not think the Taliban is all that great, only they tell them "you are so nice" "let me buy you dinner..."
In Chinese there is a saying "kou shi xin fei", in other words 'smile, shake hands, pat them on the back, but in their hearts they think 'what an SOB'... such is totally Chinese. To the West it looks reeal bad though. It looks like they might have some kind of guanxi (relationship)...still no one knows...