Please fact check anything in my response for yourself as I am not an expert, but can respond based on my personal experience.
Contribution to pension funds, provident funds and retirement annuities reduce your taxable income. As such I would assume that you could potentially be put into a lower tax bracket if you are close to the bracket starting point, but it certainly does reduce the amount of tax you pay. Both now and in future (due to your taxable amounts and rebates being lower after retirement).
You can contribute up to 27,5% or R350 000 max to retirement funding. If you increase your contribution through your company you will likely have less money paid into your bank account as a result of the amount being taken off for the increased contribution, but you will pay less tax. (there could possibly be a small area where optimisation allows for you to get more out due to going into a lower tax bracket, but it will likely not be substantial and may not be possible for everyone).
Generally if you go with a RA separate from your employer you will not get the monthly benefit in the month, but will likely get a refund at the end of the year. I say likely as this depends on what other income you have. I also say generally as you could request a tax directive that would give you the tax benefit in the same month, but this involves some admin from you and the employer and most employers try to avoid this.
Alternatives to company supplied retirement funds are available, but you need to do the calculations based on your specific scenario. Some of the things to consider include:
* Some employer funds (group funds) give additional benefits that private funds don't offer - an example is reduced life insurance (risk products) being included and access to emergency call centres
* Some employer funds limit you to certain investment choices that may impact on your diversification
* There may be noticeable differences in the fees charged in employer vs private