Is it a good idea being involved in your advisor's consulting activities as an exploratory activity during your PhD? For how long?
This could be a good thing or a bad thing. If you are being included to advance your education and it doesn't interfere with your degree progress then it is a good thing. 

If you are being exploited to the sole benefit of the advisor - slave labor - then it is a bad thing - very very bad. 

Are you free to decline? If not, then beware. Can you set your own conditions? If not, then beware. 

But, yes, these sorts of things can go on a CV: that you participated in consulting activities. 

In the US, as an early student, you are most likely involved in coursework where such activities might be less intrusive. Elsewhere, or later in the program, you need to focus on your comps and on your research. Then these things become much less likely to have value outweighing their cost to you. 

Keep your eyes open. Don't be led into traps.