An example of a harmful algae is cyanobacteria, which is a photosynthetic prokaryote and is similar to bacteria. Presence of excess nutrients, such as nitrogen and phosphorous (among other factors) help them grow and contribute to eutrophication of freshwater bodies. The algal blooms, in such settings, will cause rapid decline in the dissolved oxygen (DO) content of the water body. This DO decline will cause the death of zooplanktons, phytoplanktons and many aquatic organisms sensitive to DO levels. The cyanotoxins released by some species of cyanobacteria are also harmful to human beings through several exposure routes, including inhalation, ingestion, dermal (skin) contact, etc.
An example of a useful algae is diatoms, which are a part of family known as microalgae (cyanobacteria are also part of this family). Due to their fast growth rates, high oil content and less complex structure, they are the preferred source for biofuels. These algae can be either sourced from nature or grown in labs (in large reactors) and then chemically converted to biofuels. The declining quantity, relative monopoly and adverse environmental impacts of fossil fuels have forced us to search for alternatives and biofuels are one such viable option.
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