Here I collect some pros and cons which may help people to decide whether to use the Web interface or download the code.
They are not exclusive of course, many people may want to take advantage of both services.

Webrun
Pros:
Instant running without installation.
Easy parameter entry with context-sensitive options and explanatory text.
Parameters checked.
Powerful server to run the jobs.
Automatic management of run parameters for future use.
Some basic plotting provided.

Cons:
Cannot see working details of current version ('black box').
Data transfer may be restrictive for large/multiple runs.
Not adapted for large-scale parameter scans (this may come).
Not suitable for integration in e.g. fitting routines.
Cannot adapt for own purposes.
Run parameters restricted to those allowed by interface.
Dependence on external hardware and system.

Code
This is basically the inverse of the above.

Pros:
The details of the code are visible.
No data transfer.
More flexibility in choice of run parameters.
Free choice of run ID.
Can be modified for own use.
Can be integrated in other routines.
Parts of code can be used e.g. for plotting routines (especially reading data like Skymaps)

Cons:
Some effort to install, requires several external packages, and some configuration steps.
No parameter checking.
User must do own run management.
Requires significant CPU resources especially for 3D runs.
Need own plotting routines.

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Andy Strong, MPE