This response is likely to open up a firestorm of dissenting views, but here goes.
To be able to answer that question properly, we need to know the series and model number of your TiVo. A short summary of what is allowed would be:
All DirecTiVos require a service contract with DirecTV. These models do not work with anything but DirecTV.
Without a subscription, most Series 1 TiVos act like a VCR, requiring manual scheduling of recordings. Some of the later models do require a subscription to function. But without a subscription, you cannot schedule Season Passes or Wishlists. The TiVo must be set to manually record all programs.
All Series 2 TiVos require a subscription to receive television guide data. Also included in this would be Season Passes, Wishlists, Suggestions, MRV, TiVoToGo, Online Scheduling, etc. The only exceptions are the following models: Pioneer DVR-57H, Pioneer DVR-810H-S, Toshiba SD-H400, Toshiba RS-TX20, Toshiba RS-TX60. These models have TiVo Basic service, which only gets 3 days of guide data and does not allow any of the regular subscription services (MRV, TiVoToGo, Online Scheduling, etc.).
All Series 3 TiVos require a subscription to receive television guide data. Also included in this would be Season Passes, Wishlists, Suggestions, MRV, TiVoToGo, Online Scheduling, etc.
What is not allowed and is considered theft of service:
Any attempt to get television guide data without a subscription.
Any attempt to extract shows similar to MRV without a subscription.
I'm sure others can add to the list of "theft of service." These are all I can think of a this time. Basically, if you want a DVR that does not require a subscription to function, you do not want a TiVo.
I'm a little fuzzy on the Series 1s, as I do not own one. But I'm sure others will chime in and correct me.
Hope that helps,
robomeister