"Random deposits" are a bit like playing the lotery - especially if one is frequently chasing "hot tips". You might make it big, but the odds are vastly against you.
"Random" deposits into various investments won't be optimal, because such "random" decisions will not be properly diversified and balanced. Various investments have different rates of risk and return. "Random" deposits will not take this into account for an individual's personal situation.
In addition to needing to research individual investments as they are made, investments also need to be considered as part of a whole financial picture. A few considerations for example:
- Do you have an appropriate emergency fund?
- What is your risk tolerance? This will often largely be determined by when you are planning to retire.
- What are the tax implications of an investment? These can in some cases greatly reduce your real return.
- Are you primarily investing for income (focusing on dividends) or long term capital appreciation?
- How will the investment affect your diversification? Too much exposure to one part of the economy can leave you vulnerable if economic situations change. (For example, if 90% of your portfolio was invested in oil stocks, and the price of oil plunged, you would be in big trouble. But if your portfolio was properly diversified, you would be in much better shape)
Simply put, random isn't a financial strategy.