How much should the scrum teams commit for in sprint

Sprints are driven by commitments that a scrum team provides for the stories that it will deliver by end of sprint. This is where most of discussion is about about how efficient a scrum team is in delivery. Although I beg to differ with this practice of linking efficiency and stories committed for - I always do empower my teams to set minimal expectations and deliver maximum. I will blog on this topic in future, but for now how much time is available to plan for?

Following are the main categories of time in a sprint from planning perspective:
1. Vacation / holidays
2. Time for scrum mandatory formalities
3. Time for so called the over head activities
4. Time for unplanned
5. Net planable time

Vacation / holidays : The time when team members aren't available for work due to vacation / leaves / holidays. Some teams do maintain a calendar of leave plans and place it near standup corner.

Time for scrum mandatory formalities : The time for planning, retrospective, sprint demo and preparation time, daily stand up. 
Time for over head : The ones mandated by organization like all hands,  trainings,  meetings, any special projects from organization perspective,  recruitment, email checking  etc.  Scrum master will have to identify how much of over head is there and negotiate with stake holders to minimise them or to better organise them so as to eliminate disturbance to team's commitment. 

Time for unplanned : These activities are the ones that cannot be planned like impact of impediments,  unplanned but unavoidable meetings etc.  As the name suggests is not planable and hence reserve a effort bucket in alignment with your management and team which will not be planned. 

Net planable time : This is the capacity left over after taking away the above mentioned ones. Teams should only plan for this and provide commitment.

Art of setting impossible targets

A smart goal is something which is specific, measurable, attainable, realistic and timely. When the goals are being set, whether its personal / professional, these are some of the important characteristics. However, I have been witnessing then and there some of the most unrealistic goals in the recent past and this makes me wondering if the quality of project management is witnessing a degradation these days.

Some of the interesting ones which I did come across in past few months:
1. In one of teams, the target for the number of support tickets was increased 300% without any additional increase in capacity allocation. To make it more interesting, there were very few challengers who actually questioned this logic.
2. One of my managers set goals which were SMART in his perspective. However, they went against some of the fundamental principles of lean - be scrum master for multiple teams amounting to about 40 members, in parallel manage the product quality along with actually spend 50% of time doing actual test execution.
3. One of us had a really interesting goal - to be a product owner and be a scrum master.
4. Very interesting one was - Fixed price project was using scrum!! (its never a nice combination). To make it interesting, the target was to deliver stories worth 100% of available capacity.

If stretch becomes the baseline, will there be any motivation left to challenge oneself? If a goal is not meeting SMART conditions, its more likely to fail than succeed.