Small holder drip is always advantageous to the farmer in water conservation. At a basin scale, benefits depend on several factors. Number of farms adopting this, size of the basin, loss of water, etc could influence benefits to the basin. In any scale, it is a beneficial technology for water conservation of a basin.

Smallholders drip is grate technology for saving water and it is use in a big scale. But you need to observe the salt concentration at the end of the wet front of the drip not to be accumulated around the root zone of the plant and affect the yield. So you need every time of period to put extera water to wash away this salt.

Make an estimation of the amount of water used by irrigation in regard of the total amount of water flowing at the outlet of the basin.  For instance calculate the total surface covered by the different types of cultures and multiply by the average need of water to cover their annual PE minus the amount of rainfall.

The FAO Irrigation & Drainage Papers offers you a lot of information!

This is an interesting question. Assuming that the irrigated area will not increase as a result of the shift to drip irrigation, the basin-wide irrigation water use will decrease. However, often time, the irrigated area increases. Also, very often the cropping pattern will change as a result of adopting drip irrigation. This also might have an impact on water resources basin-wide. 

Farmers tend to expand their agricultural production, as soon as more water is available. Keep this in mind! Also, drip irrigation eliminates deep percolation, which might affect ground water flows and balances. Good luck!

Interesting question. By saving amount of water and  getting more quantity and  good quality through maintaining congenial moisture regime,small holders drip is much beneficial. With drip they can grow more remunerative crops also.

Surely drip irrigation for small holder farmer is an exciting preposition. Drip irrigation especially in perennial crops has huge potential , regardless of rained or irrigated fruit culture...

There is not a single or simple answer to your question Kbrom, it would depend on a number of factors such as: previous water use, groundwater levels, means of powering the pressurised system (assuming it's not by gravity), the type of crops to be irrigated (more thirsty than what was cropped before?), the area under irrigation, water quality......and a few more; it's often the case in irrigation, for nearly each question, there's a few depends.....the risk is when we think that a single answer cuts it and we are oblivious to the other elements of the system !