When should one not use Material design

I'm designing an admin panel.
material design has some concepts which affects both UI and UX.
Right now I have dilemma whether I should follow material design guidelines or craft a design which does not follow any specific guidelines.
Following material design takes creativity from one and makes the design predictable, on the other hand crafting a design from scratch brings the long process of making decisions for every possible interaction.

Is there any guidelines to detect if one should use material design guidelines on a web app?

What are pros and cons of using material design on a web app over a custom pattern?

Also Is there any cost (in the manner of time and designing interactions) choosing to design a custom theme over material design?